The invention relates to tires that have improved high speed properties.
Conventionally tires are loaded with high surface area carbon black to provide good tear strength and increase the modulus of the rubber. A high level of the carbon black, however, causes the tires to have a high hysteresis, which contributes to a high rolling resistance, which works against high speed properties.
In the conception of the present invention, it was proposed that if the level of carbon black was reduced, and the omitted carbon black was replaced with a filler material that reduced the hysteresis of tire components in the crown area of the tire while maintaining stiffness, that rolling resistance could be improved, with a complementary improvement in high speed properties.
It is an object of the present invention to provide a tire with improved high speed properties.
Other objects of the invention will be apparent from the following description and claims.
A pneumatic tire is provided comprising a pair of axially spaced apart annular beads, carcass plies wrapped around the beads, reinforcing belt plies disposed over the carcass plies in a crown area of the tire, gum strips disposed between edges of the belt, and an overlay disposed radially outward of the belts, tread disposed radially outward of the overlay, and sidewalls disposed between the tread and beads. The elastomer of the belts, overlay and gum strips comprises a polymer blend of 2-15 parts by weight thermoplastic reinforcing polymer per 100 parts by weight tread rubber (2-15 phr). In the illustrated embodiment, the polymer blend has a 100% modulus of 5.5 to 7.5.
The improved properties described herein are observed when the reinforcing polymer is mixed into the rubber used in the crown area reinforcement (the belts, gum strips and overlay) in a two step process where reinforcing polymer domains are predeveloped in a master batch as a first step in the process. Also, the improved tire properties described are observed only when the reinforcing domains are in all three components of the crown area reinforcement as described above.
In illustrated embodiments, the thermoplastic reinforcing polymer is polyamide or polypropylene, and the elastomer comprises polybutadiene, polyisoprene, styrene/butadiene copolymers, and mixtures thereof. The thermoplastic reinforcing polymer may be grafted to the tread rubber using a grafting agent.